In an unusual case, a Halifax pediatrician has had his license suspended for improperly administering vaccines, a "complex" situation for officials.

Dr. William Vitale had a habit of mixing vaccines into a single syringe rather than administering them separately, and as many as 500 children will have to be re-vaccinated.

For example, at a year old, babies receive a four-in-one vaccine – measles, mumps, rubella and varicella – along with two other vaccines to protect against meningococcal disease and pneumococcal disease. Dr. Vitale told investigators at the Nova Scotia College of Physicians and Surgeons that he mixed the three shots in one syringe to reduce the number of needles children would get.

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However, mixing the three together rather than administering them separately can render them ineffective. That's because some shots are given intramuscularly while others are done subcutaneously, and preservatives in one vaccine can inactivate the action of another.

Canadian immunization guidelines, as well as product inserts, explicitly warn against mixing. The Nova Scotia immunization schedule also tells physicians that vaccines given on the same visit should be given by a separate needle and syringe using a different injection site.

"It's astounding to me that this happened at all," Dr. Robin Taylor, medical officer of health for the province's Capital Health Authority, said in an interview. She noted that, paradoxically, Dr. Vitale's actions will result in children actually getting more needles.

Dr. Taylor said her priority is remediating the situation to ensure all children are protected against infectious diseases. But fixing the problem will be complex because it's not entirely clear who got the mixed vaccines, and there's no simple of way of testing who has immunity to various diseases.

To be safe, authorities have said that all of Dr. Vitale's pediatric patients from 1992 to 1994 and from 2003 to the present may need to be re-vaccinated. (Those dates are when, according to the schedule, more than one vaccine was to be administered so theoretically they could have been mixed.)

The health authority has set up a hotline, staffed by public health nurses, to offer advice to parents and it is making shots available free of charge.

One key question remains unanswered: How did Dr. Vitale carry out the practice of mixing vaccines for more than a decade – especially given the fact that in 2006, a parent complained that her child did not receive the recommend vaccinations, exposing the vaccine mixing problems.

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A spokesperson for the Nova Scotia College of Physicians and Surgeons could not be reached for comment. There is no online record of a formal complaint having been made to the College, nor any indication of an investigation or formal action.

The process began on Dec. 13, when the College published a terse notice that Dr. Vitale's license had been suspended, which only came to the attention of the public two weeks later when public health officials held a press conference to inform parents.

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